1. Field of the Invention
This invention relates to a light axis adjusting apparatus for adjusting the light axis of a headlamp according to the inclined state of a vehicle. This invention is preferred, particularly when applied to a truck having a cab and a cargo bed provided on a frame.
2. Description of the Related Art
In recent years, high intensity lamps have been adopted from the viewpoint of safety. High intensity lamps contribute greatly to safety, but are highly likely to be dazzling to other vehicles. Thus, studies have been conducted on various technologies for adjusting the light axis of a headlamp according to the inclined status of a vehicle so as not to dazzle the driver of an oncoming vehicle.
Japanese Patent Application Laid-Open No. 1998-166933, hereinafter referred to as Patent Document 1, proposes such a light axis adjusting apparatus for adjusting the light axis of a headlamp according to the inclined status of a vehicle.
“A vehicle headlamp light axis direction automatic adjusting apparatus” described in Patent Document 1 calculates a pitch angle in a longitudinal direction of a vehicle based on signals from height sensors disposed on front and rear wheels of the vehicle; and performs filtering of the pitch angle in a driving state control mode set based on a vehicle speed and acceleration to change the response of adjustment of the light axis direction of headlamps so as not to dazzle an oncoming vehicle.
In the above apparatus of Patent Document 1, a pair of height sensors (front and rear ones) for measuring the amounts of change in the front and rear vehicle heights are used to detect the inclination of the vehicle. When this conventional apparatus is applied to a truck or the like having a cab and a cargo bed provided on a frame, the amounts of displacement between the front or rear axle and the frame are detected, and the inclined status of the cab is determined by the difference between the front and rear displacement amounts. Based on this determination, the light axis of the headlamp is adjusted.
In the truck having the cargo bed provided on the frame, however, the frame is deflected under a load of a cargo, thus making it difficult to determine the inclined status accurately. That is, depending on the position of the cargo, the vertical strokes between the front and rear axles and the frame may be nearly the same, although the frame is deflected and a front end portion of the frame (a portion on the cab side) is inclined upwards. In this case, the light axis of the headlamp needs to be adjusted so as to be directed downward. However, it may be determined that there is no inclined state, and this may make it impossible to adjust the light axis of the headlamp.
Various light axis adjusting apparatuses have also been proposed in which ultrasonic sensors are mounted at the front and rear of the vehicle instead of the height sensors, and the inclination of the vehicle is determined based on the difference in output between these front and rear ultrasonic sensors. However, the ultrasonic sensor is mounted, while exposed to the outside, at a lower portion of the vehicle. Thus, a stain such as dust or mud is liable to deposit on a signal transmitting portion or a signal receiving portion of the ultrasonic sensor. This stain may make high accuracy detection of the vehicle height impossible.